The present invention relates to AC-DC power conversion and more particularly to the use of bi-directional devices and elimination of losses due to unidirectional devices used in conventional front-end rectifier bridges.
A standard off-line AC-DC power conversion stage is usually constituted by an input or front-end rectifier bridge followed by an isolated switch mode DC—DC conversion stage. This DC—DC stage is actually a DC-AC-DC stage, in which the high frequency AC provides isolation by means of a high frequency transformer. The main reason for using the front-end rectifier bridge, which is a significant source of power losses, is that commonly available power switches are unidirectional, i.e., can block only unipolar voltage.
Similar disadvantages, including lower efficiency, high component counts, overall system complexity, and higher cost may be found in other systems using the multistage approach, e.g., circuitry using input bridge, PFC and isolated DC—DC and those using bridgeless PFC and isolated DC—DC.